Filters REST authentication errors.
This is used to pass a WP_Error from an authentication method back to the API.
Authentication methods should check first if they're being used, as
multiple authentication methods can be enabled on a site (cookies,
HTTP basic auth, OAuth). If the authentication method hooked in is
not actually being attempted, null should be returned to indicate
another authentication method should check instead. Similarly,
callbacks should ensure the value is
null before checking for
A WP_Error instance can be returned if an error occurs, and this should
match the format used by API methods internally (that is, the
data should be used). A callback can return
true to indicate that
the authentication method was used, and it succeeded.